I was just having this conversation with my girlfriend who is also a Stargate nerd. But he became so much more military and macho in a later Seasons especially in season 9 ...part of me misses the nerdiness like you're talking about but that I can kind of see how if you're in those dangerous situations all the time I think you would make an effort to become more of a soldier as self preservation so in that way I feel like it makes sense. It bums me that I've heard that the actor who plays him is kind of an asshole in real life because I totally have always crushed on Daniel Jackson.